1. Field of the Invention
The present invention relates to a storage device system (hereafter referred to as a “storage system”) for storing data used by a computer in a computer system. More specifically, the present invention relates to a control method of a storage system by which a host computer (hereafter referred to as a “host”) is connected to one or more other storage systems, and the storage areas in the other storage systems (“hereafter referred to as a “device”) are virtualized as a device of its own.
2. Description of the Related Art
The amount of data received/transmitted by computers has remarkably increased as information systems are rapidly developing, for example, expansion of the internet business, computerization of procedures, and the like. In addition to such remarkable increase in the amount of data, the amount of data to be stored in storages such as disk-to-disk backup or long term storage of business activity records (transaction information, mail, or the like) of corporations in response to, for example, dealing with audits, is also increasing rapidly. Accordingly, in corporation information systems, while enhancing storages of every aspect/every system is pursued, management of IT infrastructure, which has become more complicated, is searching for an efficient and simplified system. In particular, there has been a rising expectation to the technology that seeks to optimize the total cost using the optimal storages according to the value of data.
One of the approaches to reduce the management cost of systems with large scale storage is the storage virtualization technology disclosed in JP-A-2005-011277. The above document discloses a storage virtualization technology (hereafter referred to as an “external storage connecting technology”) wherein a first storage system is connected to one or more second storage systems, and devices to be provided by the second storage systems to upper level devices such as hosts are provided to the hosts as a logical device of the first storage system (hereafter referred to as a “logical device”) through the first storage system. The first storage system, when receiving an input/output request of the logical device from the host, determines the target access device corresponds to which device between the logical device of the second storage system and a physical device such as a disk device contained in the first storage system (hereafter referred to as a “physical device”), and, pursuant to the outcome of the determination, distributes the input/output request of an appropriate access destination.
The storage system utilizing the external storage connection technology disclosed in JP-A-2005-011277 enables a system in which a plurality of storage systems each of which having differing attributes such as performance, reliability, cost, and the like are collected. For example, an optimal data allocation pursuant to the up-to-date and value of the data is enabled by connecting the first storage system having high cost, high functionality, and high reliability which utilizes the external storage connection technology to the second storage system having low cost, low functionality, and low reliability, and structuring the tiered storage areas. By using systems with storages having different storage layers, for the purpose of preparing for audits, or the like, a large amount of information such as transaction information, mail, or the like, that is generated during everyday business can be stored in a long term storage at optimal cost in response to the value of each information.
However, as described above, when a large amount of data is stored for a long time, i.e., several decades during the life span of the storage, the devices constituting the computer system are needed to be replaced in the middle of the data storage period. In particular, JP-A-2005-011277 discloses a migration method by copying the data of the device managed by the first storage system of the migration source to the first storage system that will be the migration destination of the newly introduced data. However, when the conventional input/output processing of the device performed by the first storage system, the data copy processing may be adversely affected, for example, a decrease in output. Furthermore, the large amount of device data that will be migrated needs to be copied in its entirety, consequently, a large amount of time is necessary for the device transfers between the first storages.
Furthermore, it is expected that, in a system having a storage dealing with a large amount of data such as in large scale data centers, from the perspective of securing performance, a plurality of the first storage systems may be connected and managed in the system. In such a system, since each of the first storage systems virtualizes the large amount of data belonging to the second storage system, workload imbalance between the first storage systems may be increased depending on the fluctuation in the input/output workload to each of the devices (hereafter, input/output to the device is also referred to as “I/O”).